The present invention relates to a pneumatic tire for a bicycle. A bicycle pneumatic tire comprises on respective left and right sides thereof a bead, each of which has a bead core. A carcass, preferably, a carcass having diagonally oriented cords, is disposed such that each respective end of the carcass is wound about one of the bead cores. The carcass is comprised of at least one cord ply (which is preferably folded and arranged such that multiple cord layers are produced). A xe2x80x9ccord plyxe2x80x9d is a rubber layer or sheet reinforced by reinforcements such as cables or cords and these cables or cords are arranged within the cord ply such that substantially all of them in a cord layer extend parallel to one another. The bicycle tire of the present invention comprises, in addition to the afore-described constituent elements, sidewalls which extend along the exterior of the carcass in a wear protecting manner within the axial edges of the tread of the tire.
The bicycle tire of the present invention is particularly adapted for fitment as a bicycle tire for so-called xe2x80x9cmountain bikesxe2x80x9d, otherwise known as off road capable bicycles. With such mountain bicycle tires, in addition to low weight, minimal ground surface pressure, and decreased rolling resistance, a relatively high wear resistance is desirable such that, during cycling through thorny bushes or underbrush or the like, the chances of a tire failure are reduced to the greatest possible extent.
In the historical development of the fabrication of carcasses for pneumatic tires, the deployment of a full weave type of carcass stands as the starting development. Tires of such constructionxe2x80x94which engendered relatively low production costs as a result of the reduced number of pliesxe2x80x94beneficially revealed, as a function of their own relatively low weight, a more than adequate carcass structure for withstanding the effects of the interior air overpressure. However, the durability of such carcasses was relatively modest.
After several years, tire designers recognized that the intersection locations of a full weave carcassxe2x80x94in other words, the locations where one cord (either a warp or weft cord) overlapped an orthogonally oriented respectively opposite weft or warp cordxe2x80x94led to wear or chafing through of cords. This recognition led to a turning away from full weave carcasses in tire construction and the development of a functional separation: each former full weave carcass construction was replaced with a pair of layers which comprised one respective layer with reinforcements having right side increasing reinforcement strength and the other respective layer with reinforcements having left side increasing reinforcement strength. With regard to the rubber layer or sheet having the therein embedded, parallel extending reinforcements, the term xe2x80x9ccord plyxe2x80x9d is used while the term xe2x80x9ccordxe2x80x9d or xe2x80x9ctire cordxe2x80x9d is used to refer to the yet to be covered in rubber arrangement of the cords.
The above noted approach avoided the creation of cord intersection locations at which reinforcement cords crossed one another without the presence of rubber therebetween. The preferred configuration of diagonal cord carcasses fabricated in this manner should therefore comprise at least two cord layers, whereby, in one of the cord layers, all reinforcement cords increase in one given direction and, in the contiguous cord layer, all reinforcement cords increase in the direction opposite to the one given direction.
As viewed from the perspective of slip movement associated with tire delamination in tractive settings and the hysteresis of the tread material, a portion of the rolling resistance of a tire occurs in its sidewall due to the periodic compression, expansion, and bending of the sidewall rubber during the travel of the tire. The technical development of premium tires thus evolved toward ever decreasing amounts of rubber in the sidewalls and this effect can be particularly noted in the xe2x80x9cskinwallxe2x80x9d tire models which have come into use in racing activities. In these types of tires, the only rubber to be found in the sidewalls is the rubber added during the calendaring of the cord weave with the rubber mixtures.
The rubber covering of the carcass cords at the sidewall periphery above the thickest location of cords is only a few microns or micrometers thick. As a result of this thinness, the carcass cords are visible through the sidewall, whereby the carcass appears naked or as a xe2x80x9cskinxe2x80x9d.
Such tires permit the achievement of a reduced weight and a relatively low rolling resistance in comparison to xe2x80x9cgum-wallxe2x80x9d tires in which the carcass in the sidewall region is covered on its respective axial outer side with an additional rubber layer which contains, without fail, carbon black.
Another measure to reduce rolling resistance of tires of the upper quality tire segment includes the use of reinforcements having ever increasing elongation resistance properties, thus permitting the use of thinner reinforcements and, correspondingly, a thinner application of the rubber layer in which these reinforcements are calendared or embedded. A substantial reduction in rolling resistance can be achieved in particular with mountain bike tires subjected as they are to discontinuous travel paths. The customers of such tires are willing to pay for the increased cord density per tire necessitated by the thinning of the cords.
Unfortunately, the problem consequently occurs that the carcass reinforcements are increasingly susceptible to wear in correspondence with their decreasing thickness.
The susceptibility of the cord reinforcements in such tires to wear can, to be sure, be compensated for by the provision of a thick rubber layer (gum-wall) but this tends to defeat the advantages of such tires as the amount of rubber in the sidewall is increased by this compensation approach and, as a result, the rolling resistance is increased.
One object of the present invention is to fabricate a sidewall configuration for a bicycle tire, in particular, a mountain bicycle tire and, especially, xe2x80x9cskinwallxe2x80x9d type embodiments of such tires, such that the bicycle tire substantially approaches the reduced weight and minimized rolling resistance of the conventionally known skinwall tire while at the same time substantially approaching the high wear resistance of a rubber walled tire.
In connection with the individually enumerated aspects, the objects of the present invention are accomplished by:
providing a textile sheet structure (1.9), which is especially preferably a ply, as wear protection in the sidewall region on the outside of the carcass,
the textile sheet structure having cords (1.91) extending in two cord directions oriented substantially perpendicular to one another,
whereby both of the cord directions are diagonalxe2x80x94in other words, at an angle of 30 to 70 degrees with respect to the circumferential direction, and
whereby the textile sheet structure is not wound about the bead cores (1.2).
The orientation of the cords diagonally not only saves weight but, additionally, the respective cords in a left hand textile strip for wear protection on the left sidewall and the respective cords in a right hand textile strip for wear protection on the right sidewall which comprise the wear protection textile sheet structures are scarcely extended or elongated by virtue of full inflation of the cured tire.
Preferably, the extension or elongation of the two lamellar textile sheet structures by virtue of the inner tire pressure are substantially completely precluded. This is achievable if the green uncured tire is inflated after the disposition thereon of the two textile sheet structures but before linking or vulcanization (which transform the initially plastic uncured rubber into elastic rubber); this procedure leads to small plastic displacements of the cords of the wear protection textile sheet structures relatively along the thus inflated carcass cords that, on the cured tire, the cords of the wear protection textile sheet structure are only first put in tension upon reaching such inflation pressure as exceeds the pressure imparted during the inflation of the green uncured tire during the procedure just described.
Because the cords of the wear protection textile sheet structure are not at all or, at most, not substantially, loaded by the inner tire pressure, it is particularly recommended that the inflation pressure imparted during the inflation of the green uncured tire is selected to be approximately as high as the working inflation pressure of the cured tire.
The wear protection textile sheet structures of the present invention avoid the necessity of being wound about the bead coresxe2x80x94which would otherwise be called for in view of the further tire building engendered by the addition of the wear protection textile sheet structuresxe2x80x94so that no fretting occurs at the cord intersections of the wear protection textile sheet structures during the lifetime of the racing bicycle tire (which was the reason that decades ago full weave webs fell out of usage for tire construction) because the cord intersections of the wear protection textile sheet structures are barely subjected to any pressure or force.
According to a further aspect of the tire of the present invention, an additional increase in the resistance to tear propagation is achievable by integrally interconnecting each cord with the other respective cord at the cord intersections where the cords cross one another (as in a web or full weave) or are wound about one another (as in a loop or hoop web). Such interconnections can be implemented by means of adhesives but are more preferably implemented through melting together of the intersecting cords under pressure.
An integral interconnection of cords at a cord intersection can be advantageously effected, according to a further additional aspect of the tire of the present invention, by.configuration of the wear protection textile sheet structure as a web. This configuration as a web can be achieved by initially disposing two mutually perpendicular cord frameworks, each having internally parallel, preferably monofilament, cords, in superposed relationship on one another. Thereafter, the superposed cord frameworks are pressed together between two heated plates or heated rollers to a combined thickness which approximates the cord thickness, preferably 5 to 10% greater than the cord thickness. The temperature of the press plates or rollers should be just above the melting or softening temperature of a cord. In this manner, a melting together of intersecting cords at cord intersections can be achieved which thereby leads to increased resistance to tear propagation. A construction such as just described will be referred to herein as a xe2x80x9cwebxe2x80x9d.
A web appears exactly as a full weave when viewed in top plan view in that each angular image appears as if it is flat. Another example of a webxe2x80x94fabricated to be sure of steel cord, not textile cordxe2x80x94are the steel mats in steel reinforced concrete.
The web of the tire of the present invention can advantageously be configured as a full weave structure. It is necessary with this configuration, as well, that the cords are integrally interconnected with one another at the cord intersections. This can be achieved by disposing the full weave structure so that it is pressed together between two heated plates or heated rollers to a combined thickness which approximates the cord thickness, preferably 5 to 10% greater than the cord thickness. The temperature of the press plates or rollers should be just above the melting or softening temperature of a cord. In this manner, a melting together of intersecting cords at cord intersections can be achieved which thereby leads to increased resistance to tear propagation.
The present invention also contemplates that the textile sheet structure can be configured as a hoop structure, preferably as a hooped knit structure. It is again recommended that the locations at which the cords are in contact with one anotherxe2x80x94in this instance, the cord intersectionsxe2x80x94should be integrally interconnected with one another. This can be achieved by disposing the hoop structure so that it is pressed together between two heated plates or heated rollers to a combined thickness which approximates the cord thickness, preferably 5 to 10% greater than the cord thickness. The temperature of the press plates or rollers should be just above the melting or softening temperature of a cord. In this manner, a melting together of intersecting cords at cord intersections can be achieved which thereby leads to increased resistance to tear propagation.
In accordance with more additional aspects of the present invention, the textile sheet structure arranged in the tire sidewall, which is preferably a full weave or a loop structure and optimally a web, offers substantially the same protection from wear as the known gum-walls of tires have offered. The wear resistance of the tire of the present invention is also surprisingly high, to the degree that tensile strain in the cords does not at all occur or, at most, barely occurs; if instead the cords of the textile sheet structure were elongated by the pull exerted thereon by carcass cords and thereafter subjected to the inflation pressure, not only would the durability of the textile sheet structure be reduced, as noted, but also the sought after wear resistance would be reduced.
The textile sheet structure, in contrast to the gum-walls, contributes relatively less to the tire weight and, above all, to the rolling resistance. The present invention thus provides bicycle tires which in terms of weight and rolling resistance are only relatively slightly less performant than skin wall tires and which in their resistance to wear are practically at the level of gum-wall tires. The tires of the present invention are therefore ideal for use as mountain bicycle tires.
The fabrication of tires of the present invention involves configuring a textile sheet strip at a width which approximately corresponds to the curved length of a sidewall cross section. The textile strip section, which is delivered by the textile manufacturer, is cut in cut directions diagonal to a cord direction. The strip from which the webs are cut should be approximately 1.2 meters wide in order to preclude having to dispose piece work elements around the tire circumference.
In the building of the cords into the textile sheet structure by the known method of diagonal construction in which the cord plies are laid up on a smooth surface drum, the beads are set, and the plies are wound therearound, the two diagonal cut full weave strips are deliberately wound a single time around the tire circumference before the setting of the tread strips andxe2x80x94in the event that a belt is also to be setxe2x80x94before the setting of the topmost belt. The ends of the strips can be butt connected to one another without overlapping.
In accordance with yet another aspect of the present invention, the cords of the wear protection textile sheet structures are preferably covered with rubber although only with a substantially sheer thickness. The rubber thickness should, over the extent of a cord, have a value at the most of 90 microns and preferably, a value of between 50 to 60 microns. A very thin rubber coating of this type facilitates the setting of the wear protection textile sheet structure on the carcass onto which it is laid up, leads to a higher delamination resistance of the textile sheet structure with respect to the carcass in the cured tire, and can minimize the ozone and ultraviolet (UV) attacks on the textile sheet structure which arise during tire usage. Moreover, a very thin rubber coating of this type reduces the build up of dirt during submersion of the textile sheet structure.
A very thin rubber coating of the type described can be achieved by coating of the textile sheet structure in a rubber solution before the laying up of the textile sheet structure on the tire build. This rubber solution can be achieved by spraying or immersing or painting. An especially good result with particularly low solution emissions appears to be achievable by means of immersion and thereafter removing excess solution by blade or squeegee. A benzene free ligroine having light petroleum fractions is recommended as a solvent. The application of the very thin rubber coating by calendaring is necessarily not practical.
In the following description of another aspect of the present invention, the term xe2x80x9cwide dispositionxe2x80x9d or xe2x80x9cwide applicationxe2x80x9d of the wear protection web is to be understood to mean: the distance from cord intersection to cord intersection (in the case of a web) or, respectively, from cord wrap to cord wrap (in the case of a weave) should be at least 4 times and, preferably, 5 times as great as the thickness of the cord; this is for the reason that the thickness of the cord, subjected to the heat and pressure associated with the creation of the cord intersections, is not constant and is, therefore, stopped at the least thickness between a pair of cord intersections or cord wraps. The absolute distance between a pair of cord intersections or cord wraps should, in dependence upon the cord thickness, be at a value between 0.8 to 3 mm and, in particular, at a value preferably between 1.3 and 1.8 mm.
It is to be understood that relatively thinner cords should be disposed relatively more closely to one another than relatively thicker cords. In this regard, the cord thickness, in dependence upon the magnitude of its loading, should be between 0.2 to 0.7 mm and, in particular, should be preferably 0.4 mm. This preferred cord thickness of 0.4 mm is particularly efficacious in connection with the preferred cord distance of between 1.3 to 1.8 mm.
A particularly favorable relationship between the increasing wear resistance, on the one hand, and the tire weight, the rolling resistance, and cost, on the other hand, is available if the warp and weft cords are formed of nylon 6.6. It appears to be possible to employ monofilament up to a thickness value of 0.4 mm, monofilament having an especially good wear resistance capability in relationship to its weight. The use of polyfilament for relatively thicker cords appears to be necessary in order to preclude the occurrence of a too large stiffness property in the sidewalls.
Many commercially available textile sheet structures exhibit a different strength in one cord direction than in the other cord direction; this is particularly the case with full webs in which the warp is dimensioned stronger than the weft. For this reason, the warp cords may be thicker and/or less tightly twisted and/or at a greater cord density than the weft cords. Analogous configurations are also possible with a weave. It is known that a non-uniformity in the cords in both cord directions contributes to a further increase in the wear resistance of the tire whose slip direction is established such as, for example, through an appropriate sidewall indication.
With regard initially to a free rolling tire, it can be observed that sinking into an aggressive tractive setting at the beginning will effect high wear on the tire sidewalls as compared to climbing out of the aggressive tractive setting at the end thereof. As viewed from the perspective of the beadxe2x80x94which is appropriate for the reason that the local anchoring of the wear protection thereat is stiffer than at the tread surface edgexe2x80x94it can be observed that all cords of the textile sheet structure forming the wear protection are under stress. If a random initial release or tear has occurred somewhere thereon, the tire pressure thereagainst becomes a delamination force.
With regard now to a driven rear axle tire, it can be observed that there is slip against the drive direction. This means that the cords which increase in the direction of rotationxe2x80x94these are the cords which extend in the rotation direction as one follows the cord from radially inside to radially outside the tirexe2x80x94are loaded under greater pressure than the cords in a free rolling tire. Accordingly, the cords which increase in the counter rotational direction are subject to relatively less pressure and delamination force.
For this reason, it is advantageous, with respect to a rear drive tire designed to rotate in a preferred direction, if the stronger and/or more densely arranged cords of the wear protection are the cords which increase in the direction of rotation and the weaker and/or less densely arranged cords of the wear protection are the cords which increase in the counter rotational direction.
With regard now to a braked front tire, it can be observed that a slip occurs in the drive direction. This means that the cords which increase in the counter rotation direction are more strongly subjected to pressure than those of the free rolling tire.
Consequently, the cords which increase in the rotation direction are subjected to relatively less pressure and delamination force. For this reason, it is advantageous for a front tire designed to rotate in a preferred direction, if the stronger and/or more densely arranged cords of the wear protection are the cords which increase in the counter rotation direction and that the weaker and/or less densely arranged cords of the wear protection are the cords which increase in the rotation direction.
The prior discussion is also applicable to the construction of the sidewalls of the tire.
The warp and weft cords of the wear protection web can be fabricated in differing colors to aid in foreclosing mistaken selection of the appropriate wear protection web during tire construction.
The present invention has applicability to tires adapted to enclose tubes as well as tubeless tires; tubeless tires may be preferable due to reduced rolling resistance and less abrupt pressure loss properties.
A tire tube must necessarily be formed of a rubber mixture substantially comprising natural rubber in order to responsibly limit the rate at which a tear will grow in the event of a tire failure. In particular, racing tiresxe2x80x94which are subjected to relatively high speeds and corresponding longer braking travel until brought to a stopxe2x80x94must often be constructed with natural rubber in lieu of butyl rubber with the butyl rubber""s attendant beneficial thickness property and this leads to the situation wherein the tube walls must be formed of relatively large thickness to compensate for the effect of the relatively thin formation capabilities of the natural rubber for wall thickness. The total weight of the tire is correspondingly increased which leads, in turn, to increased rolling resistance.
In correspondence with the synergistic effect of the high wear resistance of tires constructed in accordance with the present invention and thickness build up which reduces the risk of pinching, the thickness of the halogen butyl impermeable or sealing liner disposed on the tire interior can be beneficially held to a thin dimensionxe2x80x94for racing tires, preferably to a value on the order of 0.3 mm; for other tires, to a value on the order of 0.5 mm. The halogen butyl rubber with its known high impermeability capability can thus even be deployed, in spite of its mechanical sensitivity, on mountain bike tires which are subjected to high performance challenges.
According to another advantageous aspect of the present invention, the textile sheet structure which reinforces the sidewall extends into the bead region of the tire and this offers the opportunity to omit the customary bead protecting belt or band which typically provides wear protection with respect to the rim flange on which the bead is mounted. Correspondingly, the tires constructed in accordance with the present invention can be constructed with the most avant garde configurations which are often sought by the sport challenge seeking purchasers of skinwall type tires. A tire constructed in accordance with the present invention characteristically features a carbon black free sidewall rubber (which permits an especially low rolling resistance performance) and a relatively reduced rubber thickness which lends a half transparent appearance to the tire.